Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$89.77	8.476%	$97.3789	$97.38	$97.40	$97.40
Purchase #2	$141.72	9.259%	$154.8419	$154.84	$154.85	$154.80
Purchase #3	$26.35	10.700%	$29.1695	$29.17	$29.15	$29.20
Purchase #4	$226.83	8.584%	$246.3011	$246.30	$246.30	$246.30
Purchase #5	$51.28	6.177%	$54.4476	$54.45	$54.45	$54.40
Purchase #6	$63.87	13.345%	$72.3935	$72.39	$72.40	$72.40
Purchase #7	$184.38	6.603%	$196.5546	$196.55	$196.55	$196.60
7 purchase totals =	$784.20		$851.0871	$851.08	$851.10	$851.10